1. Field of the Invention
This invention relates to a device for retrieving tools lost in petroleum wells. More specifically, the present invention is an improvement of present fishing tools suited for use through tubing in cased hole wells.
2. Description Of The Related Art
There are various methods of completion and production of an oil well, gas well, or the like. Regardless of the method utilized in a particular well, there will invariably be a well casing and production tubing installed in the well. The well casing is essentially a pipe that is installed into the borehole for substantially the entire depth of the well. Casing is typically from 8 to 14 inches in inner diameter, depending on the diameter of the drill bit used to drill the well.
Production tubing is a tubing of smaller diameter, typically about 2 to 4 inches in inner diameter, that is set in a portion of the well somewhat concentric with the casing. The tubing allows communication of the producing zone of the well with the surface. The tubing is held in place by packers that are essentially elongated toroids with an outer diameter close to the inner diameter of the casing and an inner diameter close to the outer diameter of the tubing.
After the tubing and casing are installed in the borehole there is often need for various procedures to be performed on the well, such as gamma ray correlation to open hole electric logs, perforation, and the like. These procedures are performed by tools that are attached to what is known as a wireline. The wireline is a cable with a plurality of electrical conductors contained therein. The tools are lowered into the well on the end of the wireline and activated or monitored at the surface by an operator.
Occasionally, for various reasons, a tool becomes detached from the wireline and is lost in the well. Many times these tools are very expensive pieces of electronic instrumentation and/or have radioactive sources contained therein and must be retrieved. This procedure of retrieving the lost tool is known as fishing. The fishing tool has a "grappling" mechanism, or latching device, and is also lowered into the well on the end of a wireline.
The cased-hole wireline tool must be able to ascend through the tubing into the casing, where tools are typically lost. This presents a problem. In order to be able to ascend through the tubing the diameter of a fishing tool must be smaller than the inner diameter of the tubing. Thus, the fishing tool cannot cover the whole diameter of the casing. For example if the lost tool is decentralized, because it is leaning against the casing or it is stuck to the casing for various reasons, the fishing tools of the prior, due to their small diameter, art will most likely pass right by the lost tool without catching the lost tool in its grappling mechanism.
Expansible wings have been utilized in the prior art on devices adapted for oil-field fishing in order to allow a fishing tool to cover the entire diameter of a well bore. In particular, U.S. Pat. No. 366,445 to Rathbone discloses a tool for open-hole fishing used on the end of drill pipe. Since the Rathbone tool is run on the end of drill pipe, a drilling rig must be in place. This is not typically the case after a well has been completed and it would require great expense to locate a rig at a well for such a purpose. In addition even if a rig were located at the well site the Rathbone tool is not capable of being constructed in a diameter small enough to allow it to ascend through tubing. Indeed, the drill pipe is too large and the hinge and pin method of attaching the wings on Rathbone is too bulky. For these reasons, the Rathbone fishing tool is suited solely for fishing before tubing has been installed.